An accurate assessment of barometric pressure (BP) may be beneficial for improved operation of a vehicle. For example, diagnostic functions and engine strategies benefit from having an estimate of barometric pressure. However, including a BP sensor in the vehicle may increase vehicle cost. In some examples, BP may instead be inferred from existing sensors on the vehicle such as a manifold absolute pressure (MAP) sensor. For example, BP may be inferred as the MAP sensor reading plus a small pressure drop across a throttle of the engine.
One example approach is shown by Sanyal et al. in U.S. Pat. No. 6,430,515. Therein, BP is based on an output of a MAP sensor and a pressure drop across the intake system, the pressure drop based on mass air flow. However, the pressure drop and mass air flow relationship may assume a fixed physical geometry for the intake system. Since the throttle position affects the physical geometry of the intake system, the BP may only be calculated when the throttle position is above a predetermined threshold position.
However, the inventors herein have recognized various issues with such an approach. As one example, determining the BP based on the MAP sensor output and the pressure drop across the intake system may only be accurate at larger throttle openings such as wide open throttle (WOT). Thus, the BP estimate may have decreased accuracy during engine operation wherein the throttle is partially closed (e.g., at smaller throttle angles). As a result, engine control based on BP may be less accurate during conditions when the throttle angle is below a threshold throttle angle.
In one example, the issues described above may be addressed by a method for, during throttle angles less than a threshold and while an engine is carrying out combustion, adjusting an operating condition of the engine based on barometric pressure, the barometric pressure based on a current manifold pressure relative to a reference manifold pressure at a current throttle angle and reference barometric pressure. For example, a ratio of the barometric pressure (BP) at a current altitude (at which the vehicle is operating) to the BP at a reference altitude (e.g., the reference BP) may be substantially the same as a ratio of manifold pressure (MAP) at the current altitude (e.g., current MAP) to a MAP value calculated at the reference altitude (e.g., reference MAP). The reference BP may be based on a measured MAP (e.g., measured with a MAP sensor) at wide open throttle (WOT), a measured MAP at engine key-on (e.g., engine start-up), or a pre-determined BP at a reference altitude (e.g., BP at sea level). Further, the reference MAP may be determined based on one or more of a current throttle angle, the reference BP, engine speed, mass air flow, and/or cam position. As such, the reference MAP may be determined at the reference BP and current throttle angle (or mass air flow). Additionally, during throttle angles greater than the threshold, the method may include determining BP based on the current MAP (e.g., measured by the MAP sensor) and a pressure drop across an intake throttle. An engine controller may then adjust the operating condition of the engine, such as cylinder air charge, air-fuel ratio, spark timing, and/or EGR flow, based on the determined BP. In this way, BP may be determined at any throttle angle of the intake throttle, thereby resulting in more accurate and consistent engine control.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.